
Applied Math Applied Math Forum 
 LinkBack  Thread Tools  Display Modes 
August 12th, 2015, 08:02 AM  #1 
Newbie Joined: Dec 2010 Posts: 19 Thanks: 0  How many triangles in this picture?
Hi, all. I just thought of that kind of question and tried to count it. Please see the picture below. Finally got 42. Can anyone help me confirm the answer, please? Thank you very much. Last edited by Kavesat; August 12th, 2015 at 08:04 AM. 
August 12th, 2015, 08:37 AM  #2 
Senior Member Joined: Feb 2010 Posts: 704 Thanks: 138 
I think I agree ... 42. Call the lower left vertex A and the lower right vertex B. Then there are 30 triangles with A as vertex, 24 triangles with B as vertex and 12 triangles with AB as a side (that is, both A and B as vertices). By the inclusionexclusion principle the total is 30 + 24  12 = 42. 
August 12th, 2015, 09:18 AM  #3 
Global Moderator Joined: Dec 2006 Posts: 20,373 Thanks: 2010 
42


Tags 
picture, triangles 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
picture  goodfeeling  Algebra  4  November 23rd, 2013 10:00 PM 
How many discontinuities in this graph *picture attached*  kahf1_01  Calculus  1  October 29th, 2011 09:52 AM 
Picture Frame  symmetry  Algebra  4  October 3rd, 2011 02:41 AM 
a picture question  roflchopter  Algebra  1  May 4th, 2011 07:42 PM 
Solve for x, picture included  hellxfire  Calculus  2  May 14th, 2009 05:29 PM 